This section is intended to introduce various aspects of the art, which may be associated with the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Natural petroleum typically includes elements such as, for example, nickel (Ni), vanadium (V), molybdenum (Mo), iron (Fe), cobalt (Co), rhenium (Re), gallium (Ga), osmium (Os), uranium (U), thorium (Th), lead (Pb), or a combination thereof. Various ones of these elements may be so-called major elements, in that they are present in significant concentrations in a given sample, or they may be so-called trace elements.
Elements found in petroleum are typically present in a variety of isotopes. As a well-known example, naturally-occurring uranium often includes at least two isotopes: U-238, which has 92 protons and 146 neutrons; and, in much lower concentrations, U-235, which again has 92 protons but only 143 neutrons.
For various reasons, some of which are described below, major and trace elements occurring in natural petroleum are of interest in the Upstream sector of the petroleum industry (which refers generally to activities relating to the extraction of natural petroleum from deposits). In addition, in the Downstream sector (which refers generally to activities relating to the refining of natural petroleum into specific products such as gasoline, plastics, and the like), certain elements may be analyzed and monitored because of their potential detrimental effects (e.g., potential for disrupting catalytic processes).
Analysis of the elemental and/or isotopic “signatures” of major and trace elements may also be beneficial. Generally speaking, a “signature” of a given sample of material consists of the relative concentrations and/or ratios of various specified elements and/or elemental isotopes. Such signatures can provide important information about the sample. Various kinds of signature analysis are used, for example, in the identification of source environment-of-deposition (EOD) and in oil-oil and oil-source-rock correlation.
Much prior research in this area (for example in oil-source correlation or maturity studies) has tended to focus on the metallic elements nickel (Ni) and vanadium (V). This appears to be due to two factors.
First, Ni and V are commonly abundant in petroleum hydrocarbons. That is to say, Ni and V are commonly abundant in the organic fractions of petroleum, which refers to groups of organic compounds that are associated with natural petroleum such asphatenes, NSO (nitrogen-sulfur-oxygen) fractions, etc. As one illustration of the meaning of the term “associated with” as used in this disclosure, an element, for example Ni or V, is associated with an organic fraction if (i) the element is part of an organic molecule such as a porphyrin (e.g., a nickel porphyrin); or (ii) the element is not part of, but is present with and perhaps bound to, an organic compound.
Second, Ni and V tend to be primarily associated with organic fractions of petroleum and not with inorganic fractions. This largely-binary distribution of Ni and V helps to reduce the potential confusion and ambiguity of analytical results. That is, data obtained from analysis of the elemental signatures of Ni and V are very likely to be associated with organic fractions and not with inorganic fractions in the petroleum sample.
As is well-known to those of ordinary skill in the art, some inorganic fractions associated with petroleum products are aqueous (i.e., water-based), while others are mineral-based. Furthermore, inorganic fractions can be natural in origin, anthropogenic (i.e., human-originated), or a combination of the two.
While Ni and V are among the most-commonly studied elements in this area, they are not the only elements in petroleum that are of potential analytical interest. Certain other elements found in petroleum may also be associated with organic fractions. Some of these other elements include, for example, molybdenum (Mo), iron (Fe), cobalt (Co), rhenium (Re), gallium (Ga), osmium (Os), uranium (U), thorium (Th), and lead (Pb).
When these “other elements” are associated with asphaltene fractions in petroleum, they are typically related directly to the source rock from which the petroleum was generated (i.e., in which the petroleum was created). Such elements therefore could be useful for oil-oil and oil-to-source-rock correlation studies, petroleum dating, and petroleum fluid alteration studies.
However, unlike Ni and V which tend to be associated primarily with organic fractions of petroleum, these “other elements” can be associated not only with organic fractions but also inorganic fractions. Such inorganic association may also be useful. For example, information about water in the petroleum formation and/or anthropogenic inorganic contaminants may be obtained via analysis of these “other elements” in associated aqueous fractions. This lack of a binary distribution, however, can make it difficult to assess which elemental and/or isotopic signatures arise from organic fractions and which from inorganic fractions. Such difficulty, in turn, can complicate or even effectively preclude the use of these “other elements” in the kinds of applications just mentioned. Accordingly, it would be desirable to have a method for separating petroleum samples containing hydrocarbon-soluble elemental species of interest, to facilitate differentiation between organic and inorganic elemental species in signature analysis of natural tracers (i.e., deconvoluted analysis of elemental and/or isotropic signature).